The present invention relates to ultrasound imaging and therapy. In particular, drug delivery is enhanced through application of ultrasound energy.
In four to six hours after a stroke, physicians attempt to clear the thrombus which caused the stroke. When the thrombus can be cleared within this time frame, patients often recover completely. Typically, an anticoagulant drug is administered to dissolve the thrombus. A thrombus tends to harden over time and may become to stiff for a drug to dissolve. The thrombus may then be removed by the invasive use of a catheter. Catheterizing a patient who recently received an anticoagulant drug is an extremely high risk procedure. Various companies have proposed using ultrasonic energy to assist thrombolysis using high intensity focused ultrasound (HIFU).
A combination of drugs and ultrasound are disclosed in U.S. Pat. Nos. 5,490,840 and 6,165,440. Some chemotherapy drugs are designed to target tumors in response to ultrasound. Ultrasound acoustic energy is applied to cause tissue vibration, heating or cavitation. The tissue vibrations, heating or cavitation release the drug or increase the effectiveness of these chemotherapy drugs while minimizing side effects. In the examples above, a high intensity therapeutic ultrasound transmission device which does not produce images is used. If ultrasonic images are needed, then a second device, dedicated to ultrasonic imaging, is required in addition to the therapeutic device.
In U.S. Pat. No. 5,523,058, Umemura et al. propose an ultrasound system used to create cavitation and for imaging. Cavitation is created through the interaction of transmitted ultrasound energy at a fundamental frequency and a second harmonic of the fundamental frequency. A special transducer is described for this purpose.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below include a method and system for both enhancing drug uptake by application of therapeutic transmissions of acoustic energy and imaging a region to help guide the therapy with a same transducer and ultrasound system. An ultrasonic image of a field of view is generated while localized delivery of a drug is enhanced with ultrasound energy. Using the same transducer and ultrasound system reduces costs and increases system availability for a broader range of medical practitioners. For example, a single linear array of transducer elements is used for application of both imaging and therapeutic ultrasound. As another example, a transmitter is provided that transmits therapeutic transmissions having substantially equal positive and negative peaks at the face of the transducer and also is operable to transmit imaging acoustic energy. As yet another example, therapeutic pulses of acoustic energy are transmitted to have greater power for heating than imaging, but a mechanical index or pressure comparable to imaging transmissions. For example, a mechanical index of about 1.9 or lower is provided, such that cavitation of blood or other non-contrast agent is avoided.
Further aspects and advantages of the invention are discussed below in conjunction with preferred embodiments.